I have the K40, not the Calibre version, and I love it. It works, its awesome, the LEDs are on the instrument panel in front of me and invisible to the naked eye unless they are flashing.
On the turnpike here in NJ, troopers are very fond of pacing you from your blind spot. No radar can save you from that, but alertness will.
On slower speet limit roads, like 25mph, or 35mph a radar is invaluable and super effective, because thats the only way they can get you, they can't pace you. A lot of people who knock radar detectors because they don't "really" speed don't understand that a ticket for 50 in a 25 is the same as a ticket for 90 in a 65.
I know that Valentine has a religious following and I'm sure its great. They do have a patent on direction indicators. But the K40 people have gotten around that by having different LEDs for front & rear alerts.
My vote is K40. Installed its the most invisible and seemless solution, imo.
I have had this 911(997) for 6 months and the one before it (996) for 18 months. I have been pulled over once and I did not get a ticket. Both 911s had a hardwired K40.
Here's that story if you'd like to read:
http://www.surfpoet.com/archives/category/wheels/One of the final things i negotiated with my salesperson when I ordered my 997 was that they split the cost of the K40 with me, so that was cool.